The present invention relates, in general, to electronics, and more particularly, to semiconductors, structures thereof, and methods of forming semiconductor devices.
In the past, the electronics industry utilized various methods and structures to control light sources such for example an LED light source. In some applications, an LED driver for driving LEDs connected in a series string may have used floating switches, which can selectively short ones of the LEDs. Such switches were sometimes used to individually control light intensity produced by each LED, for example by using PWM dimming. Each LED could be controlled separately and the intensity of each LED could be controlled in the range from one hundred to zero percent (100% to 0%). The switches could also be used for shaping of the light beam.
In some embodiments, the switches may have been floating relative to ground potential. In one embodiment, they could be constructed as MOS transistors or alternately as high voltage MOS transistors. In some applications it was difficult to charge the intrinsic gate-to-source capacitance of the MOS transistors to a voltage sufficient to enable the MOS transistor. In other embodiments, the gate-to-source voltage may not be formed very accurately and the MOS transistor may not be properly enabled.
Accordingly, it is desirable to have a method and apparatus to enable the MOS transistor, or to form a more accurate gate-to-source voltage, or to charge the gate-to-source capacitance to a sufficient voltage to enable the MOS transistor.
For simplicity and clarity of the illustration(s), elements in the figures are not necessarily to scale, some of the elements may be exaggerated for illustrative purposes, and the same reference numbers in different figures denote the same elements, unless stated otherwise. Additionally, descriptions and details of well-known steps and elements may be omitted for simplicity of the description. As used herein current carrying element or current carrying electrode means an element of a device that carries current through the device such as a source or a drain of an MOS transistor or an emitter or a collector of a bipolar transistor or a cathode or anode of a diode, and a control element or control electrode means an element of the device that controls current through the device such as a gate of an MOS transistor or a base of a bipolar transistor. Additionally, one current carrying element may carry current in one direction through a device, such as carry current entering the device, and a second current carrying element may carry current in an opposite direction through the device, such as carry current leaving the device. Although the devices may be explained herein as certain N-channel or P-channel devices, or certain N-type or P-type doped regions, a person of ordinary skill in the art will appreciate that complementary devices are also possible in accordance with the present invention. One of ordinary skill in the art understands that the conductivity type refers to the mechanism through which conduction occurs such as through conduction of holes or electrons, therefore, that conductivity type does not refer to the doping concentration but the doping type, such as P-type or N-type. It will be appreciated by those skilled in the art that the words during, while, and when as used herein relating to circuit operation are not exact terms that mean an action takes place instantly upon an initiating action but that there may be some small but reasonable delay(s), such as various propagation delays, between the reaction that is initiated by the initial action. Additionally, the term while means that a certain action occurs at least within some portion of a duration of the initiating action. The use of the word approximately or substantially means that a value of an element has a parameter that is expected to be close to a stated value or position. However, as is well known in the art there are always minor variances that prevent the values or positions from being exactly as stated. It is well established in the art that variances of up to at least ten per cent (10%) are reasonable variances from the ideal goal of exactly as described. When used in reference to a state of a signal, the term “asserted” means an active state of the signal and the term “negated” means an inactive state of the signal. The actual voltage value or logic state (such as a “1” or a “0”) of the signal depends on whether positive or negative logic is used. Thus, asserted can be either a high voltage or a high logic or a low voltage or low logic depending on whether positive or negative logic is used and negated may be either a low voltage or low state or a high voltage or high logic depending on whether positive or negative logic is used. Herein, a positive logic convention is used, but those skilled in the art understand that a negative logic convention could also be used. The terms first, second, third and the like in the claims or/and in the Detailed Description of the Drawings, as used in a portion of a name of an element are used for distinguishing between similar elements and not necessarily for describing a sequence, either temporally, spatially, in ranking or in any other manner. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments described herein are capable of operation in other sequences than described or illustrated herein. Reference to “one embodiment” or “an embodiment” means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment, but in some cases it may. Furthermore, the particular features, structures or characteristics may be combined in any suitable manner, as would be apparent to one of ordinary skill in the art, in one or more embodiments.